Chromium oxychloride reacts violently on phenol, producing hydroquinone ether, O(C 6 H 4 OH)2; chromic acid gives phenoquinone, and potassium permanganate gives paradiphenol, oxalic acid, and some salicylic acid (R.
All four mono-hydroxyxanthones are known, and are prepared by heating salicylic acid with either resorcin, pyrocatechin or hydroquinone; they are yellow crystalline solids, which act as dyestuffs.
7-dihydroxyxanthone, known as euxanthone, is prepared by heating euxanthic acid with hydrochloric acid or by heating hydroquinone carboxylic acid with 3-resorcylic acid and acetic anhydride (S.
7-trihydroxyxanthone, is found in the form of its methyl ether (gentisin) in gentian root; it is obtained synthetically by condensing phloroglucin with hydroquinone carboxylic acid.
Of such syntheses we may notice: the condensation of sodium malonic ester to phloroglucin tricarboxylic ester, a substance which gives phloroglucin or trioxybenzene when fused with alkalis, and behaves both as a triketohexamethylene tricarboxylic ester and as a trioxybenzene tricarboxylic ester; the condensation of succinic ester, (CH2 C02C2H5)2, under the influence of sodium to succinosuccinic ester, a diketohexamethylene dicarboxylic ester, which readily yields dioxyterephthalic acid and hydroquinone (F.
HO 2 C CCI:CCI CO CC1 3 ' - > H02C CC1:cC1 c02H+CHe13' (to) (xi) Hydroquinone (1.4 or para-dioxybenzene) (1) gives with chlorine, first, a tetrachlorquinone (2), and then hexachlor-p-diketo-R-hexene (3), which alcoholic potash converts into perchloracroylacrylic acid (4).
It crystallizes in tables which melt at 140° C. and boil at 267° C. When heated with 10% hydrochloric acid to 180 C. it yields hydroquinone (J.
Quinhydrone, C 6 H40 2 -C 6 H 4 (OH) 2, is formed by the direct union of quinone and hydroquinone or by careful oxidation of hydroquinone with ferric chloride solution.